The ease with which an oxy-acetylene or an oxy-hydrogen outfit may be set up where needed, and the small size of the blow pipe and its flexible rubber-hose connections, make such an outfit very practical and convenient for use on work which demands local heating.

In making a weld, two sheets of metal are butted edge to edge in a clean, close-fitting joint as shown at A, Fig. 265. Two blowpipe flames are held at a and b on opposite sides of the plates, directly opposite each other, and a short length along the seam is heated to welding heat. With one of the pieces properly supported to hold it firmly in place, the other may be struck with a hammer to bring about the weld through the closer contact due to the blow.

Another method of welding is shown at B, Fig. 265. A sheet of metal rolled to cylindrical form presents its edges in V-shape as at c. These edges are temporarily held together by bolts and straps.

A blow-pipe flame is directed into the joint to bring it to welding heat, and at the same time a heavy wire of pure Norway iron is held so that the flame melts its end. The drops of fused metal from the wire run into and fill the joint, resembling the process of soldering, until the entire notch is filled with solid metal. The joint should be hammered while hot to restore the grain size of the fused metal and increase its strength. The joint needs no particular cleaning nor any flux before welding; is begun.

A thicker sheet of metal may be cut at the edges to form a joint as at d, and is welded along the upper notch and then rolled halfway around and welded along the lower notch.

A poor joint will result if the operator allows drops of metal to fall upon a part of the seam not heated to welding temperature.